[boy8cookie]

I want to build an ultra portable USB Hub, with at least 4 ports. Each of the four ports needs to provide the 500mA power to the device attached. I don't want to plug the hub into a wall outlet, instead I want to power it via firewire. I haven't seen anything like this, but I don't believe it's out of the question. I have a basic understanding of electronics, but I haven't worked with USB or Firewire at all.

I'm basically just looking for any insight on how I can make this work... Budget is around $100 US. I'll probably start by trying to mod a basic USB Hub that uses an external power supply to work off a modded firewire cable.

[Waragainstsleep]

Thats how I'd do it too.
Here is the pinout for firewire. USB pinouts are on the same site if you want them but all you need is the power output of the adaptor that comes with the hub. Almost certainly 5V, not sure the current it handles.

FireWire (IEEE1394) bus interface pinout and signals @ pinouts.ru

[boy8cookie]

Ahh, nice, thanks for the link

[Dork.]

The FireWire power pin that is listed as "Unregulated DC; 30 V no load" should give you some pause, as you're probably not going to be able to connect the Firewire power directly to the USB power. You'll have to put a voltage regulator in there to generate the 5V from whatever is coming in on that power line.

[boy8cookie]

Good point! Something like this should do the trick, right?

RadioShack.com - Cables, Parts & Connectors: Component parts: Transistors & analog ICs: +5V Fixed-Voltage Regulator 7805

[Dork.]

Probably, although without looking at the datasheet I can't be sure. You might want to buy cheap USB and FireWire hubs to act as a buffer between your experiment and your computer, just in case. If somethign goes wrong and you burn out an upstream port, it would suck if that port was on your Mac....

If you're looking for places other than Radio Shack for components, try:

Digi-Key Corporation - USA Home Page
Mouser Electronics - Electronic Component Distributor

Watch out, though, since the shipping will kill ya!

[boy8cookie]

Good point on the buffer, luckily I'm testing on an iBook G3 that was recently replaced by a MacBook so I'm not worried. What I've decided I want to do is put a 6 pin Firewire port on the USB hub that connects to DC input of the hub, through the +5V Fixed-Voltage Regulator. This should let me use a normal 6pin - 6pin firewire cable to power the device. Does that make sense?

[boy8cookie]

Well I went ahead and tried this, and it worked! I took some (terrible) pictures to showcase my (sloppy) work
USB Hub - a photoset on Flickr

[DCJ001]

Here's a part that would be a big help for you for less than $21.00:

Amazon.com: D-Link DUB-H7 High Speed USB 2.0 7-Port Hub: Electronics

[Waragainstsleep]

Nice. Looking good.

[Tesselator]

Originally Posted by boy8cookie 

Well I went ahead and tried this, and it worked! I took some (terrible) pictures to showcase my (sloppy) work
USB Hub - a photoset on Flickr

I like that you modified something you already had instead of buying more and more plastic
junk. By looking at the photo Flickr Photo Download: Uncased! it seems that there could be
some "cold-solder" happening there. If later on the power becomes intermittent or cuts out
open it back up and use some flux on the connections. Also if you seem to be having trouble
with overheating the parts in order to get the solder to flow you may want to choose a smaller
gauge wire.

[boy8cookie]

Yeah, the solder job is pretty bad, I've managed to get it a bit cleaner with a hotter iron. The solder in that pic was done with one of those cold-heat battery powered irons, which I'm not very happy with. I was able to create a pretty solid connection with a better iron and the hub is still working great.